We are studying the relation of histone subtype switches to the generation of chromatin diversity and the control of cell multiplication during embryogenesis and tissue differentiation, in the sea urchin and mouse. We are also studying the roles of subtype-specific histone H1 phosphorylations in these processes. The relation of the various subtypes to the formation of non-dividing cells will be explored by a comparison of the subtypes in mitotic chromosomes (i.e. dividing cells) with those in total embryo chromatin, as well as by a combination of immunofluorescence and autoradiography. Associations among subtypes will be studied by the use of cross-linking agents. The relation of chromatin conformation to histone subtypes and their various phosphorylated forms will be studied in nuclease digestion experiments. We will examine the histone subtypes and their phosphorylated forms in different tissues and developmental stages by 2-dimensional electrophoresis. To explore the relation of H1 function to the structure and phosphorylation state of the molecule, we will compare the primary structures and phosphorylation sites of different H1 subtypes. We hope to gain insights into molecular events underlying basic processes of normal development, including the founding of cell lineages, the generation of non-dividing cells and the maintenance of a population of dividing cells. Such information is pertinent to the understanding of developmental defects.